People often desire that a single article be capable of use in different modes. For example, a weapon capable of firing a relatively high powered round may be modified or adapted to accept a round of the same caliber but having a smaller shell casing. These smaller rounds cost less so that practice firings on rifle ranges become much more economical. A number of U.S. Pat. Nos., such as 4,169,329; 4,058,922; 3,776,095, are directed to such conversions.
A different type of weapon conversion involves a weapon that is specifically designed to be used either as an airgun or as a firearm. This type of convertible weapon allows the user the choice of firing either inexpensive pellets or darts as well as more expensive, but more powerful, cartridges. U.S. Pat. No. 127,873 discloses a weapon which can be used as either a firearm or an airgun. U.S. Pat. No. 2,605,756 discloses a device mounted within the breech of a firearm to allow the weapon to be used as an airgun. However, neither of these patents disclose a weapon which can be easily modified to tailor the chamber and bolt face for the particular firing mode to be used, as well as to the particular cartridge or gas powered projectile used. It is obvious that a chamber which is designed for housing a cartridge will probably not be the optimal configuration for use with a pellet or dart. Further, chamber configurations for pellets may be different for optimal functioning compared to that for a dart. Similarly, cartridge casings for different types of rounds of ammunition often call for a different chamber size even though the bullet is the same diameter.